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        <p>创建NSString的分类，用来获取字符串的字节长度<br>用两种方法实现</p>
<figure class="highlight objc"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//</span></span><br><span class="line"><span class="comment">//  NSString+VCHProperty.h</span></span><br><span class="line"><span class="comment">//  SmartWatch</span></span><br><span class="line"><span class="comment">//</span></span><br><span class="line"><span class="comment">//  Created by chenhui on 2016/11/22.</span></span><br><span class="line"><span class="comment">//  Copyright © 2016年 vhuichen. All rights reserved.</span></span><br><span class="line"><span class="comment">//</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#import <span class="string">&lt;Foundation/Foundation.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">@interface</span> <span class="title">NSString</span> (<span class="title">VCHProperty</span>)</span></span><br><span class="line"></span><br><span class="line">- (<span class="built_in">NSUInteger</span>)convertToByteLength;</span><br><span class="line">- (<span class="built_in">NSUInteger</span>)asciiLength;</span><br><span class="line"></span><br><span class="line"><span class="keyword">@end</span></span><br></pre></td></tr></table></figure>

<p>实现方法</p>
<figure class="highlight objc"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//</span></span><br><span class="line"><span class="comment">//  NSString+VCHProperty.m</span></span><br><span class="line"><span class="comment">//  SmartWatch</span></span><br><span class="line"><span class="comment">//</span></span><br><span class="line"><span class="comment">//  Created by chenhui on 2016/11/22.</span></span><br><span class="line"><span class="comment">//  Copyright © 2016年 vhuichen. All rights reserved.</span></span><br><span class="line"><span class="comment">//</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#import <span class="string">&quot;NSString+VCHProperty.h&quot;</span></span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">@implementation</span> <span class="title">NSString</span> (<span class="title">VCHProperty</span>)</span></span><br><span class="line"></span><br><span class="line">- (<span class="built_in">NSUInteger</span>)convertToByteLength &#123;</span><br><span class="line">    <span class="built_in">NSUInteger</span> selfLength = <span class="number">0</span>;</span><br><span class="line">    <span class="type">char</span> *p = (<span class="type">char</span> *)[<span class="keyword">self</span> cStringUsingEncoding:<span class="built_in">NSUnicodeStringEncoding</span>];</span><br><span class="line">    <span class="built_in">NSUInteger</span> encodingLength = [<span class="keyword">self</span> lengthOfBytesUsingEncoding:<span class="built_in">NSUnicodeStringEncoding</span>];</span><br><span class="line">    <span class="keyword">for</span> (<span class="type">int</span> i = <span class="number">0</span>; i &lt; encodingLength; i++) &#123;</span><br><span class="line">        <span class="keyword">if</span> (*p) &#123;</span><br><span class="line">            selfLength++;</span><br><span class="line">        &#125;</span><br><span class="line">        p++;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> selfLength;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">- (<span class="built_in">NSUInteger</span>)asciiLength &#123;</span><br><span class="line">    <span class="built_in">NSUInteger</span> selflLength = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">for</span> (<span class="type">int</span> i = <span class="number">0</span>; i &lt; <span class="keyword">self</span>.length; i++) &#123;</span><br><span class="line">        <span class="type">unichar</span> uc = [<span class="keyword">self</span> characterAtIndex:i];</span><br><span class="line">        selflLength += isascii(uc) ? <span class="number">1</span> : <span class="number">2</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> selflLength;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">@end</span></span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p>经测试两种方法都可以获取到字符串的字节长度</p>

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